This invention pertains to catalyst rejuvenation to remove deposited metal contaminants, and pertains particularly to a catalyst rejuvenation process for removal of such metal deposits from spent catalysts using a chemical treatment.
In coal catalytic liquefaction and hydrogenation processes, the used or spent catalyst gradually becomes contaminated by deposits of metals such as iron, titanium, calcium, sodium, silicon, etc. from the coal. These compounds form a crust around the exterior surface of the catalyst and thereby limit the diffusion of hydrocarbon molecules into the catalyst pores. Partial removal of these contaminants, particularly iron, titanium, calcium and sodium, is an essential step towards regeneration and reuse of the spent catalyst. Also, in catalytic hydroconversion processes for petroleum, tar sands bitumen, or shale oil, contaminants such as iron, nickel and vanadium are deposited on the catalyst and thereby reduces its activity appreciably, which requires catalyst replacement. Because of the high costs of such catalysts, processes to successfully rejuvenate the spent catalysts have been sought. Although some processes for carbon burnoff from used catalysts have been developed, suitable processes for the successful removal of deposited metal contaminants were apparently not available until now.